Ideas to increase range of IR proximity detection

I'd like to hear your ideas for increasing the range of proximity detection sensor that uses an IR LED & the Parallax IR detector.

I am using a Radio Shack high-output IR LED, a Parallax 40kHz IR detector [noparse][[/noparse]350-00014], and a BS2P24 micro. The LED is mounted directly above the detector so that it shines in the same "line" as the detector. When an object comes near, it reflects the IR from the LED back to the detector.

According to its datasheet, the IR LED 276-0143 operates at 940nm wavelength and outputs 16mW @ 100mA.

The IR LED is connected, in series with a 470 ohm resistor, to an output pin in the BS2p. It is controlled using the FREQOUT command [noparse][[/noparse]FREQOUT, pin, 1, 37500].

The IR detector is connected to an input pin on the BS2p and is read using the IN command.

This system can detect an object at a range of about 6 inches from the LED/detector, but beyond that it doesn't "see" anything.

I'd really like to increase this detection range to about 9 or 12 inches.

Comments

You could drop the value of the 470 ohm resistor -- if the IR-LED drops 1.4 volts (you should measure this -- just turn it 'on' with the 470 ohm and see how much voltage drops across the LED) then the equation is:
V = IR. I = V/R. R = V/I
(5-1.4)/100 mA == 36 ohms. That's right, *36* ohms. THAT'LL be a bright LED. Use 50 ohms if you're scared.

Another 'classic' way of doing this is to use 2 IR-LED's in parallel, each with their own current limiting resistor.

If you do drop the value of the resistor, be careful driving it with one of the pins of the BS2! The pins on the BS2 are only rated to source 20ma and sink 25ma. Each of the two sets of pin banks can only support sourcing 40ma and sinking 50ma. At 100ma, this LED would easily burn out a pin.

To get around the current limit of the Stamp pins, use a MOSFET to switch current to the IR LED.· Driving the standard Parallax IR LED at about 1 amp will give a range of about 6 to 7 feet with the Parallax IR detector.· Using FREQOUT period of 1 with a BS2SX and taking a new reading every 15 to 20 msec, results in a very low duty cycle for the IR LED.

A schematic of my sumo robot sensors (adjustable limit up to about three feet) can be seen on http://brooksbots.com/Excuse%20II.htm·click on the schematic about a third of the way down the page.

Oh, and note you can "detune" the range a bit, if instead of using "FREQOUT IR_Pin, 1, 38750", you use "FREQOUT IR_Pin, 1, 30000".

Somebody once discovered that using FREQOUT values away from the "ideal" of 38700, you produce a signal that becomes harder and harder to detect by the IR-Detector, and thus requires a reflecting object to be closer and closer before it's detected. Through experimentation, you can even identify a few (maybe 3 or 4) "ranges", each resulting from a particular FREQOUT value.